1. Field of the Invention
The invention relates to a process for the preparation of heat-curable silicone resins by the reaction of alkoxysiloxanes with polyfunctional organic hydroxyl compounds.
2. Description of the Prior Art
Methyl and methylphenyl polysiloxane resins are known from German Patent No. 20 20 224, which have a ratio of organic groups (R) to silicon atoms of 0.95 to 1.5 and in which the remaining silicon valences are satisfied by oxygen and alkoxy groups. In these resins, the alkoxy groups may be present in amounts up to 0.75 moles of alkoxy per 100 g of resin and R represents methyl and/or phenyl residues and up to 20 mole percent of the methyl and/or phenyl residues may be replaced by vinyl residues. The resins are characterized by the fact that they are prepared by the reaction, at 10.degree. to 90.degree. C., of a halogen silane mixture, with an R:Si of 0.95 to 1.5, with a mixture consisting of
(a) tertiary, chain-shaped aliphatic alcohols with 4 to 8 carbon atoms and PA0 (b) primary and/or secondary, chain-shaped aliphatic alcohols with 1 to 8 carbon atoms PA0 R.sup.2 is an alkyl and/or phenyl group, PA0 a has a value of 1.0 to 1.5, PA0 b has a value of 0.1 to 0.7,
in which 0.4 to 0.6 moles of tertiary alcohol are used per mole of halogen linked to silicon, and 0.5 to 1 mole of primary and/or secondary alcohol is used per mole of tertiary alcohol. The reaction product may optionally be subjected to a conventional post-condensation. These methyl or methylphenyl polysiloxane resins are superior to silicone resins, which are prepared by the previously customary process of hydrolyzing mixtures of mono, di and trifunctional silanes with an excess amount of water. The resins, prepared according to German Patent No. 20 20 224 produce hard and elastic lacquer films with excellent heat stability.
The preparation of these resins has a process-engineering disadvantage in that before use, the pre-products of the resins were subjected to a post-condensation with FeCl.sub.3 and the FeCl.sub.3 must be washed out with water after the post-condensation. This requires an additional process step which also contaminates the effluent water with acidic waste materials, solvents and iron salts. It is a further disadvantage of these polysiloxane resins that their compatibility with pigments is sometimes inadequate. In addition, the thermal stability and elasticity of the lacquer films required for certain technical applications, cannot always be attained with these polysiloxane resins.
German Patent No. 21 07 471 discloses that the resin pre-products, initially produced according to the teachings of German Pat. No. 20 20 224, may be reacted with organic resin pre-products in such a manner that the SiOR groups contained in the resin pre-product react with the COH groups of the organic resin pre-products.
Since the organic resin pre-products have COH groups, the polyesters which have been indicated as being suitable are obtained by the reaction of adipic acid, terephthalic acid, isophthalic acid, phthalic acid or their esters, e.g., methyl esters, or anhydrides on the one hand, with multifunctional alcohols, such as, for example, ethylene glycol, trimethylolpropane, glycerin and pentaerythritol, on the other. Acrylic resins, epoxide resins, polycarbonates, phenolic resins, melamine resins, or urea resins with free COH groups may also be used. Alkyd resins, wich contain esters of multi-unsaturated carboxylic acids, are of particular importance.
These silicone-modified organic resins are superior to the previously produced mixed resins of the state of the art in respect to heat stability, weatherability, elasticity, moldability, resistance to yellowing, maintenance of gloss and adhesion to the substrate. However, because of their structure, they necessarily have the disadvantages brought about by the incorporation of organic resin pre-products.